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Transmission of SARS-CoV-2 in Australian educational settings: a prospective cohort study

Our take —

This study examined transmission within school and early childhood education centers before and following distance learning recommendations in New South Wales, Australia. Of 3033 COVID-19 cases in the region through May 1, 2020, 27 primary cases were identified in 25 educational settings, who had 1448 close contacts. Students and staff continued to attend while infectious for a median of 2 days, and there were 18 secondary cases identified overall across 4 settings. In these settings, staff-to-staff transmission had the highest rate (4.4% of contacts), followed by staff-to-child (1.5% of contacts), while child-to-child transmission had the lowest rate (0.3% of contacts). This study likely missed asymptomatic cases, and may underestimate the level of secondary transmission. However, it shows the low risk of transmission during school closures and other infection control policies throughout NSW.

Study design

Prospective Cohort, Other

Study population and setting

In New South Wales (NSW) Australia, the study identified children and school or early childhood education center (ECEC) staff from all confirmed COVID-19 cases in NSW. From January 25 to May 1, 2020, NSW had 3033 COVID-19 cases overall. Of these, 97 (3.2%) of the 3033 were children and 22 (0.7%) had links to an education setting (e.g. educators, ECEC staff). Because of school closures and other policies, 19 of these children attended an educational setting (school or ECEC) while infectious, and were included in the study sample. Among school staff, all 22 were identified as having attending school or ECEC during their infectious period and were also included in the study sample. Of these 41 cases identified, 27 were identified as primary cases in 15 schools and 10 ECEC settings, and using contact tracing, 1448 of their close contacts were identified, and 663 contacts were tested for COVID-19. The study was able to obtain symptom questionnaires from 288 contacts. During the study period, school attendance rates declined from 90% to 5% after distance learning recommendations were implemented March 23rd, 2020.

Summary of Main Findings

Of the 27 primary cases identified in the 25 educational settings, 15 were staff (55.6%) and 12 were children (44.4%). The median amount of time primary cases continued to attend school/ECEC was 2 days (range: 1 to 10 days). All of the primary cases had acquired the infection locally, with most exposure sources unknown, but, when known, mostly household contacts. There were 1448 close contacts monitored over the study period, and 663 (43.7%) were tested for COVID-19. Secondary transmission was identified among 4 settings (16.0%), with 3 schools and 1 ECEC, with 18 secondary cases (1.2% attack rate) identified through contact tracing in the schools/ECECs. Among 288 contacts with symptom questionnaire data, 22.6% (n=65) of them developed symptoms during the 14 day quarantine. Staff-to-staff transmission had the highest rate (4.4%), compared to staff-to-child transmission (1.5%) and child-to-staff transmission (1.0%), and child-to-child transmission (0.3%).

Study Strengths

The study identified all residents of NSW who tested positive, and determined their school attendance; while this did result in a small sample size, it reduced the potential selection bias for a representative sample of the area. They were also able to have a symptom questionnaire paired with contact tracing to understand how many people went on to develop symptoms, and how many continued to attend schools/ECECs. Using a prospective study, they also were able to temporally identify how changes in school policy (such as closures) reduced transmission in NSW.

Limitations

The study had small sample sizes, likely due to school closures which reduced transmission compared to what it would have been without these measures. Many contacts were tested after developing symptoms, so asymptomatic cases are likely still missing from this assessment. There was incomplete symptom data available for most close contacts as well, which may reduce the estimated number of secondary cases identified. Similarly, schools/ECECs defined close contacts and may have used differing definitions, which would also lead to contacts not being identified and reduced estimated case numbers. Finally, in their attack rate calculation, they limited it to individuals identified through their enhanced contact tracing, and did not include secondary cases identified through the NSW Department of Health population surveillance, which may deflate the estimated attack rate if these individuals were missed in the tracing

Value added

This is one of the largest studies that examines transmission in school and ECEC settings, including before and following school closures.

This review was posted on: 20 August 2020